Cancer treatment

Stemming the brain drain

CANCER is a daunting disease, and the brain tumours known as gliomas are among the trickiest to treat. They spread rapidly and are resistant to radiation and to conventional drugs, leaving patients with little hope of survival. Until now, that is. Evan Snyder and his colleagues at Harvard Medical School reckon that they have come up with a way to get rid of gliomas—at least in rats. In a paper just published in Proceedings of the National Academy of Sciences, Dr Snyder's team has shown that gliomas can be attacked and purged using stem cells.

Most of the body's cells have a limited lifespan and a narrow job to do. Stem cells are their ancestors, and can replenish themselves indefinitely. Such versatility means that stem cells offer a new way of regenerating damaged tissues. Researchers are busy trying to turn such cells from laboratory curiosities into usable organ grafts. But Dr Snyder puts his stem cells to destructive, rather than creative, use. He has found that stem cells, harvested from the brains of normal rats and injected into those suffering from brain cancer, will home in on gliomas within days of their introduction. Once they have found a tumour, they stick to their target like glue, even piggybacking on malignant cells as these move through the body.

The Harvard team has exploited such dogged persistence by genetically engineering stem cells to make them produce a protein called cytosine deaminase. This can turn a non-toxic substance called 5-fluorocytosine into a nasty chemical called 5-fluorouracil that kills all cells, normal and malignant. Cancerous rats were then given both 5-fluorocytosine, which circulated throughout their bodies, and genetically tinkered stem cells, which made their way straight to the gliomas. Since the protein needed to transform 5-fluorocytosine could only be churned out by souped-up stem cells, only the gliomas were exposed to the poison, killing them but sparing normal tissue, which the stem cells ignored. Using this technique, roughly 80% of the cancerous cells in the Harvard rats were eliminated.

Dr Snyder reckons that stem cells have a penchant for injury of any sort, and seek out damaged tissue, such as tumours, to go about their business. This suggests that the technique might be generalised to deliver specific treatments to other diseased tissues. He is therefore eager to press ahead with clinical trials, though his reasons are as much personal as professional: his best friend, to whom his paper is dedicated, died of brain cancer. High-tech stem cells might not have saved his friend, but they may, one day, give others an alternative to despair.